feat(pagespeed): add screenshot display and expandable diagnostics

- Page screenshot thumbnail next to score gauges
- Expandable audit rows with description and detail items table
- Shows URLs, HTML snippets, wasted bytes/ms for each failing element
- AuditRow component replaces flat diagnostic rows

lib/api/pagespeed.ts

@@ -20,8 +20,12 @@ export interface AuditSummary {
   display_value?: string
   savings_ms?: number
   category: 'opportunity' | 'diagnostic' | 'passed'
+  details?: AuditDetailItem[]
 }
 
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type AuditDetailItem = Record<string, any>
+
 export interface PageSpeedCheck {
   id: string
   site_id: string
@@ -37,6 +41,7 @@ export interface PageSpeedCheck {
   si_ms: number | null
   tti_ms: number | null
   audits: AuditSummary[] | null
+  screenshot?: string | null
   triggered_by: 'scheduled' | 'manual'
   checked_at: string
 }